This is something I've thought about since I first saw the movie years ago. I've gone over different ideas in my head such as wisdom, good health and love, but I think I finally found a gift that could include all of them. After the gifts of beauty and song, I think Merryweather would have given her the gift of happiness. I think this because you can be the most beautiful person in the world, you can also have the most beautiful voice in the world, but if you're not happy, what use are those things to you? Also, a happy princess would make the rest of the kingdom happy as well to see her in such a way. If a person is happy, they learn better and have a better chance of keeping an open mind, they also tend to be healthier and get sick less often. One who is happy also has a better chance of finding long lasting love.